bench: record device clocks, temperature and power for the whole campaign

A 6-round A/B here reports side noise at the 0.01% level. Clock throttling and
thermal drift move latency by far more than that and leave no trace in
run.log, so the report comes out looking exactly as clean as a run on a stable
machine. The NV run that reproduced PR763 sampled nvidia-smi every 5s
alongside the campaign; the MUSA campaigns had no equivalent, and the parallel
plan makes it worse by heating the whole box.

telemetry.py samples through the backend, so cuda and musa emit the same
columns (index, sm_clock_mhz, mem_clock_mhz, temp_c, power_w, util_pct) and
two machines' campaigns can be read side by side. mthreads-gmi offers no CSV
query mode, so the MUSA path parses --json and strips the units glued onto
each value ("36C", "1888MHz", "477.68W"); its "Power Draw " key carries a
trailing space, matched by stripping rather than by literal.

The device comes from the backend's own visibility variable when not pinned. A
list of devices resolves to no -i at all, sampling every one, rather than
silently picking the first. Dropping the placeholder drops its flag too: a
bare trailing -i fails the sampler instead of widening it.

Telemetry is evidence, not a gate. A missing or unpermitted sampler exits
quietly with its reason in telemetry.err and the campaign runs unchanged.

backends/musa.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+from typing import Dict, List
+
 from .base import DeviceBackend
 
 
@@ -50,3 +52,50 @@ class MusaBackend(DeviceBackend):
     # Device count comes from torch.musa or MUSA_VISIBLE_DEVICES. Do not guess
     # a vendor CLI here; confirm the real listing tool before adding it.
     list_command = None
+
+    # mthreads-gmi has no CSV query mode; --json is the only machine-readable
+    # form it offers. Values arrive with their units glued on ("36C", "1888MHz",
+    # "477.68W", "87%"), so the parser strips trailing non-numerics rather than
+    # trusting a fixed suffix.
+    telemetry_argv = (
+        "mthreads-gmi", "-q",
+        "-d", "TEMPERATURE,CLOCK,POWER,UTILIZATION",
+        "--json",
+        "-i", "{dev}",
+    )
+
+    def parse_telemetry(self, raw: str) -> List[Dict[str, str]]:
+        import json
+        import re
+
+        def num(v):
+            m = re.match(r"^\s*(-?[\d.]+)", str(v or ""))
+            return m.group(1) if m else ""
+
+        start = raw.find("{")
+        if start < 0:
+            return []
+        try:
+            data = json.loads(raw[start:])
+        except Exception:
+            return []
+        gpus = data.get("GPU") or []
+        if isinstance(gpus, dict):
+            gpus = [gpus]
+        out: List[Dict[str, str]] = []
+        for g in gpus:
+            clocks = g.get("Clocks") or {}
+            power = g.get("Power Readings") or {}
+            # 键名带尾随空格（"Power Draw "），别按字面写死
+            draw = next((v for k, v in power.items()
+                         if k.strip() == "Power Draw"), "")
+            out.append({
+                "index": str(g.get("Index", "")).strip(),
+                "sm_clock_mhz": num(clocks.get("Graphics")),
+                "mem_clock_mhz": num(clocks.get("Memory")),
+                "temp_c": num((g.get("Temperature") or {}).get("GPU Current Temp")),
+                "power_w": num(draw),
+                "util_pct": num((g.get("Utilization") or {}).get("Gpu")),
+            })
+        return out
+